Abstract: Plugs for protecting internal spaces of rocket combustion chambers against moisture, dust, and other environmental factors. Each plug includes a central rod with a bracket fastened to it. The plug also includes a sleeve with radially extending structural ribs. Spring-loaded cams with rollers are securely hinged at the ends of the ribs. In addition, a spring-loaded limiter and a valve are mounted on the central rod so that they can possibly move relative to the central rod. The limiter includes a sleeve and a conical shell that are connected by rod ties. The valve includes a metal stamped conical plate that forms a gas-tight fit with the rod. A sealing ring of elastic material is positioned on a peripheral part of the plate. The set of spring-loaded cams and the limiter secure the self-mounting plug in a working position and make the valve operation independent of the operation of other plug components.